Method and composition for treating tailings

ABSTRACT

The invention relates to method and composition for treating tailings from a separation process, where bitumen is separated from mineral solids. Tailings comprise an aqueous phase with suspended solid particulate material and residual bitumen and have a dry solids content &lt;25 weight-%. The method comprises addition of a flocculating agent comprising polyacrylamide to the tailings, as well as addition of an auxiliary agent comprising ionic liquid to tailings in conjunction with the flocculating agent. Flocs, which comprise solid particulate material, are formed and the formed flocs are separated from the aqueous phase. The composition comprises a copolymer of (meth)acrylamide and an auxiliary agent comprising ionic liquid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/345,748, filed Apr. 29, 2019, now U.S. Pat. No. 11,001,761, which isa U.S. Nat'l Phase of Int'l Appl. No. PCT/FI2017/050866, filed Dec. 7,2017, which claims priority to U.S. Provisional Application No.62/431,630, filed Dec. 8, 2016, and Finnish Appl. No. 20166005, filedDec. 21, 2016, each of which is hereby incorporated by reference in itsentirety.

The present invention relates to a method and composition for treatingtailings according to preambles of enclosed independent claims.

Oil sands, which are also known as tar sands, are mixtures of day, sand,water, and heavy hydrocarbons, such as bitumen. They provide a potentialsource of hydrocarbons for petrochemical industry. However, the knownprocesses for separating and recovering hydrocarbons from oil sands areexpensive, complicated and produce significant environmental damage. Theconventional bitumen extraction methods use hot water and caustic sodato separate bitumen from sand and clay in a froth-flotation process.Tailings from the flotation process comprise water, particulate solids,such as clay, residual bitumen and natural surfactants. The result is anaqueous caustic mud-like mixture, which may still contain a significantconcentration of toxic hydrocarbons and trace elements, such as arsenic.These hazardous oil sand tailings cannot be piled, especially when thesolids content of the tailings is low. In general tailings are difficultto transport, treat or store in a safe and environmentally sustainablemanner. Similar problems may also be related to tailings originatingfrom the recovery of oil from oil shale.

Polymeric flocculants have been used for chemical treatment of difficulttailings, such as oil sand tailings, in order to dewater the tailings.Even if good results may be obtained by using polymeric flocculants,especially ultrafine solid particles having particle size less than 2 μmare difficult to separate and remain suspended in the water phase. Thewater phase which contains ultrafine solid particles cannot berecirculated back to previous process stages, because the ultrafinesolid particles may start to accumulate in the water phase and disturbthe bitumen extraction. Inorganic coagulants, such as gypsum oraluminium sulphate, have been used for improving separation of ultrafinesolid particles. However there exists a need for an improved method totreat difficult tailings, as the reduced possibilities for waterrecycling make the process water intensive and environmentallyunfriendly.

An object of this invention is to minimise or even totally eliminate thedisadvantages existing in the prior art.

Another object of the present invention is to provide an inexpensive,simple method for treating tailings, especially oil sand tailings, andfor separating liquid aqueous phase from solid particulate material.

A further object of the present invention is to provide a method andcomposition which would be effective and environmentally feasible.

A yet further object of the present invention is to provide a method,which is easy to scale up into industrial scale.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 (a-b) provides exemplary graphs of total suspended solids(supernatant solids) and rates of flocculant settlement (settling rate)of process tailings samples that were treated with ionic liquids(TMG-ROS, Ch-Iso, or Guan-Iso) and polyacrylamide 2 according toFlocculation Experiment Procedure for Comparison of Different IonicLiquids. FIG. 1(a) shows supernatant solids and FIG. 1(b) shows settlingrates for each dosage of ionic liquid.

FIG. 2 (a-b) provides exemplary graphs of total suspended solids(supernatant solids) and rates of flocculant settlement (settling rate)of process tailings samples that were treated with Ch-Iso (0-3000 g/t)and polyacrylamide 1 (80-190 g/t) according to Flocculation ExperimentProcedure for Comparison of Different Dosage Amounts. FIG. 2(a) showssupernatant solids and FIG. 2(b) shows settling rates for each dosage ofCh-Iso co-administered with increasing dosages of polyacrylamide 1.

FIG. 3 (a-d) provides exemplary settling curves of volume height of thesettling floc bed (Vol Height) recorded over time in process tailingssamples that were treated with Ch-Iso (0-3000 g/t) and polyacrylamide 1(84-188 g/t) according to Flocculation Experiment Procedure forComparison of Different Dosage Amounts. FIG. 3(a), FIG. 3(b), FIG. 3(c),and FIG. 3(d) show settling curves for each dosage of Ch-Isoco-administered with polyacrylamide 1 at dosages of 84 g/t, 105 g/t, 125g/t, and 188 g/t, respectively.

The invention is defined in the characterising parts of the enclosedindependent claims. Some preferable embodiments of the invention aredefined in the dependent claims. All described features apply both forthe use as well as the method and composition of the invention, wheneverapplicable, even if it not necessarily stated so.

In typical method according to the present invention for treatingtailings from a separation process, where bitumen is separated frommineral solids, the tailings comprising an aqueous phase with suspendedsolid particulate material and residual bitumen, the tailings having adry solids content <25 weight-%, the method comprises

-   -   adding a flocculating agent comprising polyacrylamide to the        tailings,    -   adding an auxiliary agent comprising ionic liquid to tailings in        conjunction with the flocculating agent,    -   allowing floes, which comprise solid particulate material, to        form, and    -   allowing the formed floes to separate from aqueous phase.

Typical composition according to the invention for treating tailingscomprises a copolymer of (meth)acrylamide and an auxiliary agentcomprising ionic liquid.

Typical use of ionic liquid according to the present invention is fortreating oil sand tailings together with flocculating agent comprisingpolyacrylamide.

Now it has been surprisingly found out that use of an auxiliary agentcomprising ionic liquid together with polyacrylamide flocculating agenteffectively removes solid particulate material from the aqueous phase aswell as improves the separation of the formed floes. When usingauxiliary agent, which comprises ionic liquid, it is possible to reducethe amount of used polymer while obtaining the same treatment results.

The auxiliary agent comprises ionic liquid and optionally a solvent, forexample an organic solvent, such as kerosene or the like.

According to another embodiment the auxiliary agent is free of organicsolvents.

The term “ionic liquid” is in the present context understood to be anionic salt-like material, which is liquid at temperature of <100° C. atatmospheric pressure of 101.3 kPa. Ionic liquids include two components,namely a cation component and an anion component. The ionic liquidswhich are especially suitable for use in the present invention have anegligible vapour pressure at room temperature, typically about 10·¹⁰Pa, but they can be converted into form, which has vapour pressure>0.01Pa, preferably >0.1 Pa, at 130° C. The ionic liquids are soluble inwater and insoluble in non-polar organic solvents. According to oneembodiment the auxiliary agent consists of ionic liquid.

Ionic liquids are non-flammable and thermally stable, which makes theauxiliary agent safe to handle and transport and minimizes theoccupational hazards during its use.

The ionic liquid used in the auxiliary agent is also preferablybiodegradable. In this context compounds and compositions are referredbiodegradable if they reach a biodegradation level higher than 60 wo,evaluation being based on the so-called BODS (Biochemical oxygen demandafter 5 days) or “Closed Bottle Test” (OECD 301D).

The auxiliary agent comprises preferably at least one ionic liquidprepared from an unsubsituted or substituted primary, secondary ortertiary amine, such as tributylamine; or from an unsubstituted orsubstituted pyridine, amidine or guanidine, preferably together with afatty acid or rosin acid. According to one preferable embodiment of thepresent invention the ionic liquid is prepared from substituted tertiaryamine which is choline or from substituted guanidine, which istetramethylguanidine (TMG). According to one embodiment the substitutedguanidine is 1,1,2,3,3,-pentamethylguanidine (PMG) or2-butyl-1,1,3,3-tetramethyl guanidine (BTMG).

The auxiliary agent may comprise also at least one fatty and/or resinacid. According to one embodiment of the invention the auxiliary agentcomprises a mixture of fatty acids and/or resin acids. Suitable fattyacids may be saturated or unsaturated, and they can be branched orlinear. Examples of suitable fatty acids are stearic acid, hexanoic acidand isostearic acid. According to one preferable embodiment of theinvention the fatty acid is selected from stearic acid or isostearicacid. By proper selection of fatty and/or resin acids the properties ofthe auxiliary agent may be tailored to provide optimal interaction withthe flocculating agent, which comprises polyacrylamide. According to onepreferable embodiment of the invention the resin acid is rosin acid.

According to one preferable embodiment the auxiliary agent comprisesionic liquid, which is selected from choline isostearate ortetramethylguanidine rosinate.

The flocculating agent may be added in such amount that theconcentration of polyacrylamide in the tailings is 70-90, preferably80-160, more preferably 90-120, given as g polymer/ton tailings.

In the present context “polyacrylamide” denotes a copolymer ofmethacrylamide or acrylamide and cationic, anionic and/or non-ionicmonomers, preferably a copolymer of methacrylamide or acrylamide andcationic or anionic monomers, more preferably a copolymer of acrylamideand cationic or anionic monomers.

According to one embodiment of the invention the flocculating agentcomprises a cationic polyacrylamide. Cationic polyacrylamide is acopolymer of (meth)acrylamide and at least one cationic monomer,preferably a copolymer of acrylamide and at least one cationic monomer.The cationic monomer may be selected from 2-(dimethylamino)ethylacrylate (ADAM), [2-(acryloyloxy)ethyl) trimethylammonium chloride(ADAM-Cl), 2-dimethylaminoethyl methacryla to (MADAM),[2-(methacryloyloxy)ethyl] trimethylammonium chloride (MADAM-CI),[3-(acryloylamino)propyl) trimethylammonium chloride (APTAC),[3-(methacryloylamino)propyl) trimethylammonium chloride (MAPTAC), orany combinations thereof. According to an embodiment of the invention,the polyacrylamide originates from 15-40 mol-%, preferably 20-35 mol-%of cationic monomers, calculated from total amount of monomer s used inpolymerisation.

According to another embodiment of the invention the flocculating agentcomprises an anionic polyacrylamide. Anionic polyacrylamide is acopolymer of (meth)acrylamide and at least one anionic monomer. Theanionic monomer may be selected from unsaturated mono- or dicarboxylicacids, such as acrylic acid, maleic acid, fumaric acid, itaconic acid,aconitic acid, mesaconic acid, citraconic acid, crotonic acid,isocrotonic acid, angelic acid or tiglic acid.

In the present method also a flocculating agent comprisingpolyacrylamide is added to the tailings. The flocculating agent may beadded to the tailings simultaneously but separately with the auxiliaryagent, which comprises ionic liquid. Alternatively the flocculatingagent may be added before or after the auxiliary agent.

An auxiliary agent comprising ionic liquid is added to the tailings inconjunction with the flocculating agent. As explained above, this meansthat the auxiliary agent may be added before or after the addition ofthe flocculating agent, or it may be added simultaneously, butseparately, with the flocculating agent. According to one preferableembodiment the auxiliary agent is added before the flocculating agent.

According to one embodiment of the invention the flocculating agent andthe auxiliary y agent are mixed together to form a composition in liquidform that can be added to the tailings.

According to one embodiment the auxiliary agent may be added in suchamount that the concentration of ionic liquid in the tailings is500-3000, preferably 1000-2500, more preferably 1200-2200, given as gactive substance/ton tailings.

The auxiliary agent may also comprise a plurality of, i.e. two or more,different ionic liquids.

After addition of the flocculating agent and the auxiliary agent flocs,which comprise solid particulate material, are allowed to form. Thesynergetic effect produced by the flocculating agent and the auxiliaryagent provides effective formation of floes comprising also fine solidparticulate material. Furthermore, the formed floc s settle relativelyfast, which makes their separation effective also by using conventionalsettling arrangements, such as gravity settlers. The aqueous phase,after it is separated from the formed floes, may comprises less than 2weight-%, preferably less than 1.5 weight-%, more preferably less than 1weight-%, of fine solid particulate material having diameter less than 2μm. Preferably the aqueous phase, after separation of floes, is free ofsolid particulate material having diameter >2 μm.

The formed flocs may be separated from the aqueous phase by settling,centrifugation, filtration, thin lift dewatering or with any suitableseparation technique.

According to one preferable embodiment a settled floe phase is obtained,which floe phase has a solids content of at least 30 weight-%,preferably at least 40 weight-%, more preferably at least 45 weight-%.Due to the high solids content the floe phase is easy to handle,requires less space when stored and is more convenient to pile.

In one embodiment the ionic liquid may be separated from floe phase, ifdesired, regenerated and recycled back in preceding steps in thetreating process.

The separated aqueous phase may be recycled back to the separationprocess, where bitumen is separated from mineral solids. The inventionachieves a clean aqueous phase that can be used in the originalseparation process from where the tailings originate or it may be usedin some other associated process. Alternatively the aqueous phase may bereturned to the surroundings, after optional further water treatmentsteps.

Tailings, which are treated with the present invention, originate from aseparation process, where bitumen is separated from mineral solids.Tailings may originate from a separation process involving oil sand, oilshale, oil contaminated sand or oil contaminated earth or sandcontaining crude oil. Preferable tailings are oil sand tailings. Thetailings may have a dry solids content <25 weight-%, preferably <20weight-%, more preferably <15 weight-%. According to one embodiment thedry solids content of the tailings may be in a range of 5-25 weight-%,preferably 7-20 weight-%, more preferably 7-15 weight-%. Tailings maycomprise solid mineral particles, such as clay and/or sand, havingparticle size <45 μm, preferably <30 μm, more preferably <15 μm,sometimes even <5 μm.

Tailings may comprise also residual bitumen. In the present context theterm “bitumen” is understood as a highly viscous mixture of crude oil,comprising hydrocarbons heavier than pentanes, and which mixture has aviscosity above 10 000 cP, and is non-mobile at reservoir conditions.Bitumen may have an API gravity <12°, preferably <10°, more preferably<8°. The API gravity of bitumen may be in the range of 12°-6°. Bitumenmay comprise >15 weight-%, preferably >25 weight-%, of asphaltenes. Thetotal amount of asphaltenes and resins in bitumen may be >40 weight-%,preferably >45 weight-%. Tailings may comprise <5 weight-%, preferably<2 weight-%, more preferably 1 weight-%, of bitumen, before addition ofthe flocculating and/or auxiliary agent.

EXPERIMENTAL

Some embodiments of the invention are described in the followingnon-limiting examples.

Following materials were used in experimental studies:

Ionic Liquids

Choline Isosterate (Ch-Iso): active content 51.3% Tetramethylguanidinerosinate (TMG ROS): active content 27.3% Guanidinium isostearate(Guan-Iso): active content 10.0%

Polymer Flocculants

Polyacrylamide 1: standard viscosity 3.5 cP, charge 30%

Polyacrylamide 2: standard viscosity 4.0 cP, charge 30%

Process Samples

The tailings used for the experiments were thickener feed samples froman industrial process. The tailings contained approximately 11-13%solids and less than 1% bitumen.

The water used for polymer dilution was industrial gland water, and itwas used to prepare polymer solutions at a concentration of 0.4%. Samewater was also used to dilute the polymer solutions to 0.05% directlybefore their use.

Flocculation Experiment Procedure

Flocculation experiments were done according to following procedure:

-   -   1) A bucket of industrial thickener feed tailings was vigorously        stirred to homogenize the tailings, and 150-170 g aliquots were        transferred to 250 ml plastic beakers.    -   2) The tailings aliquots in beakers were stirred with a 4-blade        pitched impellers for 60 sec at 400 rpm prior to chemical        addition.    -   3) When ionic liquid was used it was added to the tailings        aliquot and mixed for an additional 60 sec.    -   4) The chosen polymer flocculant, 0.05% solution in industrial        gland water as then added to the tailings aliquot as a single        injection.    -   5) The tailings aliquot was stirred for an additional 30 sec at        400 rpm to condition the floes and then the impeller was        stopped.    -   6) The tailings aliquots were transferred to a 250 ml graduated        cylinder and the volume height of the settling floe bed was        recorded over time.    -   7) After 10 minutes of settling, the final bed height was        recorded and the top 60 ml of supernatant was transferred into a        separate container.    -   8) The supernatant was stirred to homogenize and then a 25 g        sample was taken and measured for solids content by drying the        sample in an oven overnight at 110° C.

Comparison of Different Ionic Liquids

In FIGS. 1(a) and 2(a) the solids content (y-axis) is given in weight-%,and the shown numerical values of the y-axis should be multiplied with100%. In FIG. 3(a)-(d) the y-axis values are given as %-values, andshown numerical values of the y-axis should be multiplied with 100%.

In order to determine the affinity of different ionic liquids to thetailings the results for supernatant solids are shown in FIG. 1A andresults for settling rate are shown in FIG. 1B for three ionic liquidsTMG-ROS, Ch-Iso and Guan-Iso. Polymer flocculant used was polymerflocculant 2

From the figures it can be seen that the addition of Guan-Iso showedvery little performance change. There was a slight but noticeableimprovement with the addition of TMG-ROS, while Ch-Iso showedsignificant improvement in both results.

Comparison of Different Dosage Amounts

Ch-Iso was added at dosages of 0 g/t, 1000 g/t, 2000 g/t and 3000 g/t,while the flocculant polymer 1 dosage was between 80 and 190 g/t. Theresults the supernatant solids are shown in FIG. 2A and results forsettling rates are shown in FIG. 2B at different Ch-Iso dosages. FIGS.3A-30 show settling curves for each flocculant polymer dosage.

It can be observed that at each flocculant polymer dosage the additionof Ch-Iso improved and reduced the supernatant solids content. Thesettling rate was also improved at all doses other than 84 Wt. Thesettling curves help to demonstrate that after the ten minute settlingperiod, the increase in settling rate was coupled with an improvement insettling volume, which may result to higher underflow densities in thethickener.

As the addition of Ch-Iso improved the thickener results at a givendosage it also means that flocculant polymer dosage could be reduced,while still meeting the desired performance criteria. For example if asupernatant solids content of 1% was desired, without addition of Ch-Isothis would occur at an approximate flocculant polymer dosage of 160 g/t.After the addition of 1000 g/t Ch-Iso, 1% solids content could beachieved at a flocculant polymer dosage of approximately 105 Wt. Thismeans that the reduction in polymer dosage of greater than 30% isachieved.

Although certain embodiments and examples have been described in detailabove, those having ordinary skill in the art will clearly understandthat many modifications are possible in the embodiments and exampleswithout departing from the teachings thereof. All such modifications areintended to be encompassed within the below claims of the invention.

The invention claimed is:
 1. A composition for treating tailingscomprising a copolymer of (meth)acrylamide and an auxiliary agent,wherein: (i) the auxiliary agent comprises at least one ionic liquidprepared from an unsubstituted or substituted primary, secondary ortertiary amine, or an unsubstituted or substituted pyridine, amidine,guanidine, choline, or combination thereof; and (ii) the auxiliary agentfurther comprises at least one fatty acid, at least one resin acid, or acombination thereof, wherein the at least one fatty acid comprisesstearic acid, isostearic acid, or a combination thereof.
 2. Thecomposition according claim 1, wherein the ionic liquid is selected fromcholine isostearate or tetramethylguanidine rosinate.
 3. The compositionaccording claim 1, wherein the auxiliary agent comprises a plurality ofdifferent ionic liquids.
 4. The composition according claim 1, whereinthe copolymer of (meth)acrylamide is an anionic copolymer of(meth)acrylamide.
 5. The composition of claim 1, wherein theunsubstituted or substituted primary, secondary or tertiary aminecomprises tributylamine.
 6. A composition for treating tailingscomprising a copolymer of (meth)acrylamide and an auxiliary agent,wherein the auxiliary agent comprises at least one ionic liquid preparedfrom an unsubstituted or substituted amidine, guanidine, choline, orcombination thereof.
 7. The composition according claim 6, wherein theauxiliary agent further comprises at least one fatty acid, at least oneresin acid, or a combination thereof.
 8. The composition according claim6, wherein the ionic liquid is selected from choline isostearate ortetramethylguanidine rosinate.
 9. The composition according claim 6,wherein the auxiliary agent comprises a plurality of different ionicliquids.
 10. The composition according claim 6, wherein the copolymer of(meth)acrylamide is an anionic copolymer of (meth)acrylamide.
 11. Thecomposition of claim 7, wherein said at least one fatty acid, at leastone resin acid, or a combination thereof comprises stearic acid,hexanoic acid, isostearic acid, or at least two of the foregoing.